The present invention relates to a backlight device or a lighting device, and more particularly to a backlight device used in a field sequential display apparatus including a liquid crystal display apparatus.
Some conventional color liquid crystal displays are equipped with color filters arranged on a liquid crystal display panel. This type of color liquid crystal display needs to use at least thee pixels or cells on the liquid crystal display panel corresponding to red (R), green (G), and blue (B) as a group for produce of a color image, thereby causing difficulty in achieving a high resolution. Further, since the color filters need to be positioned highly precisely with respect to the liquid crystal display panel, the complexity of fabrication increases. Furthermore, high brightness cannot be obtained due to absorption of light by the color filters.
Besides the color filter type, a time division driving or field sequential type color liquid crystal display is known. The field sequential color liquid crystal display apparatus comprises a liquid crystal display panel and a backlight device having a plurality of colored light sources, such as red, green, and blue light sources. In this type of color liquid crystal display, the light to be projected from the backlight device onto the liquid crystal display panel is switched from one color to another synchronously with the high-speed shuttering of the liquid crystal display panel, and a color image can thus be obtained by the persistence of human vision. Since the color filter is not needed, the field sequential type color liquid crystal display can theoretically achieve three times as high resolution as the color filter type liquid crystal display apparatus.
For example, Japanese Patent Application Laid-open Publication No. 5-264,988 discloses a field sequential color liquid crystal display apparatus equipped with a backlight device comprising a plurality of fixed-type colored light sources. In this color liquid crystal display apparatus, the light to be projected from the backlight device onto the liquid crystal display panel is switched from one color to another by sequentially activating the plurality of light sources. On the other hand, Japanese Patent Application Laid-open Publication No. 2000-331,520 discloses a field sequential color liquid crystal display apparatus in which the backlight device comprises a plurality of colored light sources mounted on a rotary member. In this color liquid crystal display apparatus, the light to be projected from the backlight device onto the liquid crystal display panel is switched from one color to another by rotating the rotary member. In the backlight devices of the conventional field sequential color liquid crystal display apparatus, it is generally intended to adopt mercury fluorescent lamps, each comprising an arc tube containing a mercury-containing discharge medium as the light sources.
However, using mercury fluorescent lamps in field sequential color liquid crystal display apparatuses involves the following problems. First, as schematically shown by a broken line in FIG. 8, the light power of the mercury fluorescent lamp strongly depends on ambient temperature. Thus, neither of the above conventional backlight devices can illuminate the liquid crystal display panel with stable intensity. In particular, in the case of the backlight device of the Japanese Patent Application Laid-open Publication No. 2000-331520, the ambient temperature of each mercury-type fluorescent lamp varies widely due to the heat exchange with the surrounding air as the rotary member rotates, causing unstable light power of the mercury-type fluorescent lamp. This is because the mercury vapor pressure changes with changes in ambient temperature. Second, as schematically shown by a dashed line in FIG. 9, the light power of the mercury-type fluorescent lamp needs a certain amount of time to reach a desired level after starting power distribution to electrodes. The amount of time required is, for example, about 60 seconds. Accordingly, when mercury type fluorescent lamps are adopted in the backlight device of the Japanese Patent Application Laid-open Publication No. 5-264,988, sufficient brightness cannot be obtained when the light to be projected from the backlight device onto the liquid crystal display panel is switched from one color to another at high speed. On the other hand, when mercury type fluorescent lamps are used in the backlight device of the Japanese Patent Application Laid-open Publication No. 2000-331520, the mercury-type fluorescent lamps should be kept on continuously, thereby increasing the power consumption of the backlight device.
Therefore, an object of the present invention to provide a backlight device that can illuminate a field sequential type passive display apparatus, including a liquid crystal display apparatus, with stable brightness while reducing power consumption.